The lame-duck Republican governor has jumped into the fray by endorsing more than a dozen state primary candidates, many of them Republican legislators who now face conservative primary challenges after backing her move to expand Medicaid in 2013.

Her splashiest move came two weeks ago when she threw her support behind former Mesa Mayor Scott Smith, the most moderate of the six Republicans seeking the gubernatorial nomination.

“She threw down the gauntlet in terms of her legacy on this one,” said Arizona political analyst Mike O’Neil, who hosts “The Think Tank” on KTAR-FM in Phoenix. “She is supporting people who have supported her platform This is a big deal.”

Whether those Republicans will benefit from “Brewer’s bounce,” as 12News in Phoenix described it, remains to be seen. Ms. Brewer is boosting her endorsed candidates with funding from her Arizona Legacy PAC, but conservatives have targeted them for defeat, calling them “legis-traitors” and “Brewercrats.”

“Nobody has any idea what’s going to happen. She could win them all, she could lose them all,” said Mr. O’Neil.

According to the Alliance of Principled Conservatives, which has been encouraging primary challenges for the past year, the Republican-dominated legislature went astray to the left last year by supporting Common Core and agreeing to expand “Obrewercare.” Ms. Brewer herself also vetoed a religious freedom bill in February after coming under intense national pressure from gay groups.

Meanwhile, the gubernatorial race has boiled down to a three-way contest among Mr. Smith; state Treasurer Doug Ducey, who’s the former CEO of Cold Stone Creamery; and political newcomer Christine Jones, former legal counsel of GoDaddy.

So far Mr. Ducey leads in most of the polls, and last month he won the endorsement of the Arizona Republic, the state’s largest newspaper. The GOP primary winner will face former Arizona Board of Regents member Fred DuVal, the only Democratic candidate for governor.

“Ducey, a strong conservative, has a focus on fiscal and economic issues that would bode well for Arizona’s future,” said the July 29 editorial. “He believes a stable, financially solvent Arizona can compete favorably for jobs with other states. He is right.”

The other Republican candidates — Secretary of State Ken Bennett, former Rep. Frank Riggs and former Maricopa County Attorney Andrew Thomas — are bringing up the rear in surveys, but analysts point out that anything could happen in this year’s primary.

That’s because an unprecedented number of independent voters have request primary ballots. Under a state ballot measure approved by voters in 1998, unaffiliated voters may participate in the Republican or Democratic primaries, but only about 7 percent did so two years ago.

This year, 83,448 independents have requested primary ballots in Maricopa County, the state’s most populous county, up from the 43,500 who voted in 2012. Of those, 60 percent asked for GOP ballots and 25 percent requested Democratic ballots, according to the Arizona Republic.

The influx of independents could be a good sign for Mr. Scott, who’s the clear moderate in an otherwise conservative field. If the five conservatives split the vote, then Mr. Scott could wind up with the nomination with a slim plurality.

Tim Sifert, spokesman for the Arizona Republican Party, said 14 percent of those casting ballots in the primary as of Monday were independents, but he expects that figure to drop as last-minute Republican voters head to the polls Tuesday.

“There’s a lot of those ballots still in the hands of Republican voters. I expect that percentage [of independents] to go down,” said Mr. Sifert.